Band pass shock absorber



April 24, 1962 Original Filed Sept. 30, 1957 INVENTOR EMANUEL SCHNITZERXML 9.0%

United States Patent 3,031,182 BAND PASS SHOCK ABSORBER EmanuelSchnitzer, 926 19th St., Newport News, Va. Original application Sept.30, 1957, Ser. No. 687,310, now

Patent No. 2,928,670, dated Mar. 15, 1960. Divided and this applicationMar. 7, 1960, Ser. No. 13,398

1 Claim. (Cl. 267-64) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This application is a division of my copending application Serial No.687,310, filed September 30, 1957, issued March 15, 1960 as Patent No.2,928,670, which in turn is a continuation-in-part of my copendingapplication Serial No. 528,563, filed August 15, 1955, now Patent No.2,866,633.

This invention relates to shock struts for machine elements and the likewith particular application to shock absorbers including a pistonslidable in a fluid containing cylinder. In conventional shock absorbersof this type, when the piston moves under compression in the cylinder,the fluid is forced through a small orifice in the piston, giving riseto a damping action which is roughly proportional to the square of therelative velocity of piston and cylinder. It is apparent, therefore,that the higher the disturbance frequency or time rate of change ofloading, the more resistance the absorber exhibits to relative motionuntil at high frequencies it is, in effect, a rigid link.

One of the primary objects of the invention is to filter out, in a shockabsorber, loads from disturbances in certain frequency ranges or havingcertain rates of application while retaining the required load arrestingcharacteristics of conventional shock absorbers in the remainder of thefrequency spectrum.

Another object is to provide simplified and improved means for placingthe primary object of the invention into effect. 1

Another object of the invention is to provide means for utilizing themetering pin of the piston in a conventional piston-cylinder type shockabsorber, both as a control by telescoping displacement and as a loadfiltering device by virtue of its hollow construction permitting fluidflow therethrough.

Still another object is to provide a shock absorber sensitive not onlyto displacement of the coacting parts but to the frequency of therelative movement of the parts.

A further object is to provide an arrangement in shock absorbers inwhich parts may be removed, replaced or adjusted without the necessityof complete disassembly of the shock absorber strut.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the solitary figure of the accompanying drawing whereinis shown a fragmentary longitudinal sectional view of the shock absorberwith the metering pin fixed to and depending from the piston head withinthe cylinder.

Referring now to the drawing, a shock absorber 11 is shown adapted forinsertion between two relatively movable machine parts, not shown, suchas an airplane body and a supporting wheel, and which utilizes thehollow type pin for fluid flow. The hollow shock absorber lower cylinder12, which is filled with a fluid, not shown, such as oil, at its openupper end, is provided with an inner flange 13 with a coaxialcylindrical surface on its inner side for sliding engagement with theouter wall of the hollow shock absorber upper piston cylinder 14, which3,031,182 Patented Apr. 24, 1962 is partially filled with fluid overflowfrom cylinder 12, and partially filled with a gas, such as air. In turn,the lower open end of piston 14 is provided with a terminal externalflange 15, screwthreaded to the piston, the outer flange surface beingcylindrical and forming a sliding contact with the inner wall of hollowcylinder 12. These two flanges 13 and 15 form terminal walls for avariable sized chamber which serves as a load rate sensitive buffingmeans as described in my copending application Serial No. 686,800, filedSeptember 25, 1957, now Patent No. 2,947,386, issued August 2, 1960.

The lower open end of the piston is formed internally as a nozzle with arestricted orifice 16 and upper and lower diverging sections 17 and 18.Supported from piston flanges 15 by a spider 19 is a control unit 21.This unit has a main cylindrical section 22 coaxial with the absorbercylinder 12 and extending directly below piston orifice 16. The section22 is hollow and at its lower end is formed with an inner flange 23defining a tubular section end closure wall, terminating in a reversedterminal valve cylinder 24 of reduced diameter, the inner free end ofthis terminal cylinder, in turn, being formed with a radial valve seat25 for a check valve ball 26. The terminal cylinder 24 forms a housingfor the ball 26, a stop bar 27 being fixed across the open cylinder endto retain the ball in place. The valve seat 25, at one point, isprovided with a small axial edge duct 28 which serves to permit liquidflow through valve 25, 26 when the ball is seated in closed position.Overlying the terminal valve unit 25, 26 is a piston 29 having a maintransverse pressure surface plate 31 extending across the controlcylinder 22 directly above the terminal valve and a cylindrical skirt 32normally surrounding the terminal valve cylinder 24, the outer skirtsurface having sliding engagement with the inner surface of controlcylinder 22 forming a leak resistant obstruction to fluid flow betweenthe opposed faces of pressure surface plate 31, and the open end of theskirt resting on the terminal flange 23 of the control unit.

The upper end of control cylinder 22 is constructed to form a terminalopening of a diameter less than that of the control cylinder and aplunger or pin 33 is slidably mounted in this opening so that itprojects above cylinder 22 into and through the main piston orifice 16.This plunger is hollow to form a passage 34, and the lower plunger end,inside control cylinder 22, is expanded to form a second piston 35, thispiston having a cylindrical side wall slidably engaging the upper innersurface of the control cylinder. The plunger is constructed in twosections, a lower section 36 having a diameter such that when theplunger is in its uppermost position the flow area in piston orifice 16is at its minimum value, and an upper section 37 of lesser diameter suchthat, when the plunger is moved downwardly, it will permit an increasedflow of liquid through orifice 16. A coil spring 38 is positioned insidethe control cylinder 22 for energizing both piston 29 and piston 35 andnormally holds both pistons at the outer limits of movement, as shown.

Annular ports 39 are placed radially around the construction 41 at thetop of the control cylinder 22. A check valve of the ball type similarto lower valve 25, 26 is provided at the base of the pin inside thecontrol cylinder. This valve includes a ball 42 movable in the pinbetween an upper stop bar 43 and the valve seat 44 formed of a curvedinwardly projecting flange at the lower end of the pin.

The operation of the strut will now be described. When the two pistonand receiving cylinders 12 and 14 are telescoped together with a slowlyincreasing velocity, the pressure in the receiving cylinder 12 builds upat a slow rate, forcing fluid through the main orifice 16 around theplunger 33 into the piston cylinder 14. Fluid pressure is, also appliedto the top piston 35 in control cylinder 22, thus tending to push thispiston downwardly; and the valve ball 26 in the bottom piston is movedupwardly to close valve 25, 26. However, since the pressure rise isgradual, fluid is able to flow through valve seat slot 28 at a ratelarge enough to force piston 29 upwardly, compressing spring 38 and thusmaintaining the plunger 33 in its up equilibrium position. Fluid trappedbetween plunger 33 and piston 29 is forced upward through the ball valve42, 44 and hollow plunger duct 34 to the piston cylinder 14. It is thusapparent that, for slow rates of load application, the low pass shockabsorber of the instant invention behaves as a conventional fixedorifice shock absorber.

When the force or motion is applied rapidly to the shock absorber, fluidcannot flow fast enough through duct 28 to move piston 29 upwardly tobalance the downward force applied to plunger piston 35 through port 39.Consequently, plunger 33 moves downwardly so that the upper plungersection of reduced diameter is positioned within main orifice 16. Thisallows a rapid flow of fluid through the main orifice 16 permitting thestrut to telescope rapidly and preventing development of a large load inthe shock absorber.

When the direction of the telescoping motion is reversed so that theshock strut tends to extend, the pressure in the lower strut cylinderdrops off while that in the upper piston cylinder, by virtue of thecompressed air in the cylinder, remains high. Thus, the pressure appliedthrough ports 39 drops ofl and the pressure applied upward on the lowercheck valve ball 26 also drops off, allowing this ball to drop down,thus opening this valve. At the same time, fluid from the upper pistoncylinder 14 is forced downward through plunger 33, forcing ball 42downward to close the upper check valve. The downward pressure of uppercylinder 14 on plunger 33 forces the plunger downwardly, compressingspring 38 with the result that piston 29 is rapidly moved in a downwarddirection, thus moving fluid through the lower check valve 25, 26 intothe lower cylinder 12. This positions section 37 of plunger 33 inorifice 16, allowing fluid in the upper cylinder 14 to be returned inincreased volume through orifice 16 into the lower cylinder. When theshock strut has reached the fully extended condition, the loadingdifferential between plunger piston 35 and piston 29 disappears,allowing the compressed spring 38 to recxtend and return plunger 33 toits equilibrium position. Thus, the strut is allowed to expand rapidlyin order to re-cycle itself for subsequently applied load pulses havinglow or high rates of loading.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

A shock absorber for connection between two machine parts, comprising ahollow cylinder partially filled with fluid forming a piston connectableto one part, a hollow fluid filled cylinder forming a receiverconnectable to the other part, said piston having telescoping connectionwith said receiver, a piston head having a main orifice therein at thecompression end of said piston, a hollow plunger forming a fluid passageWay and having a free open end positioned in said main orifice, acylindrical section mounted adjacent said piston head in one of saidcylinders, said plunger having sliding connection within one end of saidcylindrical section in continuation thereof, the extremity of saidplunger within said cylindrical section being of enlarged diameter andforming a plunger piston, said one end of said cylindrical sectionsurrounding said plunger between said plunger free end and said plungerextremity of enlarged diameter being of reduced diameter and providedwith at least one opening for fluid communication between said one ofsaid cylinders and said plunger piston, a piston slidingly movable inthe other end of said cylindrical section, a closure wall at the otherend of said cylindrical section beyond said cylindrical section piston,a main opening in said closure wall, a valve mounted adjacent saidopening and adapted to close said opening with development of fluidpressure in said one of said cylinders, a bleed orifice in said closurewall, and a spring placed in said cylindrical section between saidplunger and said cylindrical section piston.

References Cited in the file of this patent UNITED STATES PATENTS2,570,362 Mercier Oct. 9, 1951

